1. Field of the Invention
This invention relates to a camera system, which has a plurality of focus detection units and makes a focus lens perform a focusing operation based on the outputs of these focus detection units.
2. Description of the Related Art
Conventional focus detection units used for autofocusing include those that make use of the phase difference detection method and those that make use of the contrast detection method.
With the phase difference detection method, the subject image that is formed from the light flux that enters through an image-taking lens is divided into two parts of light flux, the amount and direction of defocus are detected from the phase difference of the two images formed by image forming the two divided parts of light flux again, and the amount of feeding of the focus lens is determined from this defocus amount. This phase difference detection method has the merit of being wide in the range of defocus that can be detected.
Meanwhile, with the contrast detection method, the subject image formed from the light flux that enters through an image-taking lens and is made incident on an image pickup device is taken in, the high frequency components are extracted, and the focus lens is moved to find the position at which the extracted signal is maximized and bring the image plane to the focused plane in the final stage.
With this contrast detection method, though the focusing process takes a long time since the amount and direction of defocus cannot be determined immediately, the merit that focusing precision that is high in comparison to the phase difference detection method is provided, and especially with digital cameras, since the image pickup device that performs photoelectric conversion of the subject image can be used directly as the image intake part of the focus detection unit, high focusing precision can be obtained without being affected by the precision of relative positioning among image pickup devices.
A camera system has been proposed which combines the above two methods of focus detection while making use of their merits, that is, with which the focusing process is made high in speed by the phase difference detection method and focusing operation by the contrast method is performed in part to achieve focusing of higher precision.
However, with the prior-art camera system, though considerations are made in regard to a focus detection method by which high speed and high precision of autofocusing can be realized at the same time, considerations are not made in regard to the accompanying drive control of a focus lens.
For example, in the case where a focus lens is driven by a stepping motor, in order to realize high precision, the feeding amount of the lens that is driven in one step of the motor must be set to no more than the minimum pitch determined from the focusing precision, and if the pulse rate is set so that step-out of the stepping motor will not occur, the drive time for autofocus becomes long with the increase of the lens feeding amount, thus preventing the speeding up of autofocus. Thus though the prior art indicates a focus detection method for realizing high speed and high precision of autofocusing at the same time, it does not accompany a lens drive control for realizing this and thus does not adequately realize high speed and high precision of autofocusing at the same time.
An object of this invention is to perform lens drive control that is optimal for each focus detection unit in a camera system that employs a plurality of focus detection methods in combination to realize high speed and high precision of autofocusing at the same time.
In order to achieve the above object, this invention provides a camera system comprising:
an image-taking optical system, which forms a subject image from the light flux that has entered the image-taking optical system;
a first focus detection unit, which detects the focusing condition of the image-taking optical system;
a second focus detection unit, which detects the focusing condition of the image-taking optical system at a higher precision than the first focus detection unit;
a stepping motor, which drives a focus lens included in the image-taking optical system;
a control circuit, which selectively uses information based on the output from the first focus detection unit and information based on the output from the second focus detection unit to control the stepping motor; and
a rotation detector, which detects the rotation phase of the stepping motor.
The control circuit performs closed loop control, based on the output of the abovementioned rotation detector, when controlling the stepping motor using the information based on the output of the first focus detection unit, and performs open control for driving the stepping motor a predetermined number of steps at a time, when controlling the stepping motor using the information based on the output of the second focus detection unit.
Also in order to achieve the above object, this invention provides a camera system comprising:
an image-taking optical system, which forms a subject image from the light flux that has entered the image-taking optical system;
a first focus detection unit, which detects the focusing condition of the image-taking optical system;
a second focus detection unit, which detects the focusing condition of the image-taking optical system at a higher precision than the first focus detection unit;
a stepping motor, which drives a focus lens included in the image-taking optical system; and
a control circuit, which selectively uses information based on the output from the first focus detection unit and information based on the output from the second focus detection unit to control the stepping motor.
The control circuit drives the stepping motor by a 2-phase excitation method when controlling the stepping motor using the information based on the output of the first focus detection unit, and drives the stepping motor by a 1-2-phase excitation method or microstep method when controlling the stepping motor using the information based on the output of the second focus detection unit.
Also in order to achieve the above object, this invention provides a camera system comprising:
an image-taking optical system, which forms a subject image from the light flux that has entered the image-taking optical system;
a first focus detection unit, which detects the focusing condition of the image-taking optical system;
a second focus detection unit, which detects the focusing condition of the image-taking optical system at a higher precision than the first focus detection unit;
a vibration type motor, which drives a focus lens included in the image-taking optical system;
a control circuit, which selectively uses information based on the output from the first focus detection unit and information based on the output from the second focus detection unit to control the vibration type motor; and
a vibration condition detector, which detects the vibration condition of the vibration type motor.
The control circuit performs closed loop control, by which the drive frequency is controlled based on the output of the vibration condition detector, when controlling the vibration type motor using the information based on the output of the first focus detection unit, and performs control for applying a drive signal of fixed frequency to the vibration type motor, when controlling the vibration type motor using the information based on the output of the second focus detection unit.
With each of the above inventions, the first focus detection unit may be arranged to detect the focusing condition of the image-taking optical system by a phase difference detection method and the second focus detection unit may be arranged to detect the focusing condition of the image-taking optical system by a contrast detection method. In this case, information on the defocus amount may be the information based on the output of the first focus detection unit and information on the contrast (high frequency components) of the subject image that has been taken in may be the information based on the output of the second focus detection unit.
Also, with each of the above inventions, the control circuit may be arranged to control the stepping motor or vibration type motor using the information based on the output of the first focus detection unit when the information based on the output of the first focus detection unit indicates the image-taking optical system to be in an out-of-focus condition that falls outside a predetermined range, and to control the stepping motor or vibration type motor using the information based on the output of the second focus detection unit when the information based on the output of the first focus detection unit indicates the image-taking optical system to be in an out-of-focus condition that is within the predetermined range.
Also in order to achieve the above object, this invention provides a lens device which is provided with an image-taking optical system that forms a subject image from the light flux that has entered the image-taking optical system, being detachably mountable to a camera which comprises a first focus detection unit that detects the focusing condition of the image-taking optical system and a second focus detection unit that detects the focusing condition of the image-taking optical system at a higher precision than the first focus detection unit, furthermore comprising:
a communication circuit, which enable communication of information with the camera;
a stepping motor, which drives a focus lens included in the image-taking optical system;
a control circuit, which selectively uses information based on the output from the first focus detection unit and information based on the output from the second focus detection unit to control the stepping motor; and
a rotation detector, which detects the rotation phase of the stepping motor.
The control circuit performs closed loop control, based on the output of the rotation detector, when controlling the stepping motor using the information based on the output of the first focus detection unit, and performs open control for driving the stepping motor a predetermined number of steps at a time, when controlling the stepping motor using the information based on the output of the second focus detection unit.
Also in order to achieve the above object, this invention provides a lens device which is provided with an image-taking optical system that forms a subject image from the light flux that has entered the image-taking optical system, being detachably mountable to a camera which comprises a first focus detection unit that detects the focusing condition of the image-taking optical system and a second focus detection unit that detects the focusing condition of the image-taking optical system at a higher precision than the first focus detection unit, furthermore comprising:
a communication circuit, which enable communication of information with the camera;
a stepping motor, which drives a focus lens included in the image-taking optical system; and
a control circuit, which selectively uses information based on the output from the first focus detection unit and information based on the output from the second focus detection unit to control the stepping motor.
The control circuit drives the stepping motor by a 2-phase excitation method when controlling the stepping motor using the information based on the output of the first focus detection unit, and drives the stepping motor by a 1-2-phase excitation method or microstep method when controlling the stepping motor using the information based on the output of the second focus detection unit.
Also in order to achieve the above object, this invention provides a lens device which is provided with an image-taking optical system that forms a subject image from the light flux that has entered the image-taking optical system, being detachably mountable to a camera which comprises a first focus detection unit that detects the focusing condition of the image-taking optical system and a second focus detection unit that detects the focusing condition of the image-taking optical system at a higher precision than the first focus detection unit, furthermore comprising:
a communication circuit, which enable communication of information with the camera;
a vibration type motor, which drives a focus lens included in the image-taking optical system;
a control circuit, which selectively uses information based on the output from the first focus detection unit and information based on the output from the second focus detection unit to control the vibration type motor; and
a vibration condition detector, which detects the vibration condition of the vibration type motor; wherein
the control circuit performs closed loop control, by which the drive frequency is controlled based on the output of the vibration condition detector when controlling the vibration type motor using the information based on the output of the first focus detection unit, and performs control for applying a drive signal of fixed frequency to the vibration type motor, when controlling the vibration type motor using the information based on the output of the second focus detection unit.
A detailed configuration of the camera system and lens device of the invention, the above and other objects and features of the invention will be apparent from the embodiments, described below.